The present invention relates to a ceramic dynamic pressure bearing, a motor with bearing, a hard disc apparatus, and a polygon scanner.
Conventionally, as a bearing of a motor axis to be a driving source of electric machinery, a ball bearing has been more used, and in a precision machinery such as periphery machinery of computers, high speed rotation of motors has rapidly progressed, and for realizing excellent bearing performance less to cause irregularity of low rotation, abnormal sound or vibration, otherwise for prolonging service life of the bearing, a dynamic pressure bearing with intervention of a fluid as an air has been served. When, for example, a main shaft and a bearing portion disposed as surrounding the main shaft rotate around the axis of rotation, the dynamic pressure bearing supports a rotating shaft owing to dynamic pressure of the fluid occurring in a space between the outer periphery of the main shaft and the inner periphery of the bearing portion. There is also a bearing which supports faces of the main shaft or the bearing portion by dynamic pressure thrust.
By the way, as to the dynamic pressure bearing, mutual members opposing via the dynamic pressure gap do not cause contact therebetween under high speed rotation at enough high level of generated dynamic pressure, but when starting to drive at small rotation number or stopping, since sufficient dynamic pressure is not generated, the members contact each other. Materials composing parts of the above mentioned dynamic pressure bearing have ordinarily employed metals as stainless steels or those coated with resins, but metal made materials are often involved with problems of abrasion or seizure by the materials contacting when starting to drive or stopping. For avoiding such occasions, an attempt has been made to coat a lubricant layer such as a resin at parts directing to dynamic pressure gaps, but an effect is not always satisfied. Then, for sufficiently securing durability against abrasion or seizure, the members opposing via the dynamic pressure gap such as the main shaft or the bearing portion have been composed with ceramic as alumina.
However, in the above mentioned conventional dynamic pressure bearing, although parts are composed of ceramic, not a little abrasion sometimes happens when starting or stopping. Further, in the bearing supporting the thrust face by dynamic pressure such as a structure where a disc thrust plate is opposed to a thrust face of a rotating body, when the rotating body and the thrust plate contact, linking (a phenomenon that two members come into close contact due to vacuum created in the clearance therebetween) or abrasion is sometimes created.
A theme of the invention is to offer a ceramic dynamic pressure bearing less to cause abrasion when starting or stopping the rotation, and enabling to realize smooth rotation in the dynamic pressure bearing.
For solving the above mentioned problems, the ceramic dynamic pressure bearing according to the invention is characterized in that a dynamic pressure gap is formed between a first rotation member and a second rotation member relatively rotating around a predetermined axis of rotation, such that fluid dynamic pressure is generated in the dynamic pressure gap accompanying the relative rotation of the first rotation member and the second rotation member,
in at least either of the first rotation member and the second rotation member, parts including surfaces (called as xe2x80x9cdynamic pressure gap-forming surfacexe2x80x9d hereafter) directing to the dynamic pressure gap comprises an at least ceramic, and
in a ceramic matrix comprising any of alumina ceramic, zirconia ceramic and silicon nitride ceramic, said comprised at least ceramic is a compound ceramic having a structure dispersed with 15 to 70 vol % electrically-conductive inorganic compound phase having main components of one kind or two or more kinds of compounds selected from tungsten carbide, silicon carbide, conductive oxide, metallic nitride, metallic carbide, metallic boride, and metallic carbon nitride. In the metallic nitride, the metallic carbide, the metallic boride, and the metallic carbon nitride, a main component is at least any of Hf, Mo, Ti, Zr, Nb, and Ta.